The nifty tricks thread

I found this on stumbleupon, and I love it. Its about how to solve "spot the difference" games way quickly.

In a nutshell, you look at the pictures side by side, go crosseyed until you see three images, focus on the middle image until it becomes clear, and you see the differences because they overlap (kind of like when you cover one eye with your hand and you see the edges but you see through it).